Dan.
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 posted on 16/2/15 at 09:16 AM |
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wheel choice big power seven
Hi all, as some of you know I'm building a sequencual turbo saab powered indy. With all this power and torque I know getting the power down is
going to be an issue. ...
unfortunately my brakes mean I can't go for the usual recommended 13s and wide tyre choices in this rim size are somewhat limited. So I'm
looking at 15s... can get some 15 X 8.25J et0 at a very resonance price, obviously won't be the best wheels in the world in terms of quality but
I can change them later.
How will these affect my handling running et0? And will 8.25j all round cause problems? Obviously I will require some bodywork modification but
I'd rather do this than spend out 1.2k+ on a set of custom split rims atm.
Suspension wise the car is fully rose jointed front and rear. The rear suspension has been modified to raise the roll center slightly to decrease
roll and improve camber in roll, the front suspension is standard but the front chassis has been significantly strengthened.
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INDY BIRD
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| posted on 16/2/15 at 09:28 AM |
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with that size of tyre on the front it will cause tram lining for sure so you probably dont need that big on the fronts etc, but rears i ran a
9" on mine with 0 offset on 235 tyre and a 7.5 on the fronts with 215 tyre no issues.
hope that helps
sean
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Dan.
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| posted on 16/2/15 at 09:33 AM |
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Thanks that's good to know, ideally I would have smaller fronts but staggered 15s Iin 4x108 don't seem that common  ill keep looking but
least these are an option.
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steve m
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| posted on 16/2/15 at 01:08 PM |
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Just for info, I used to have 13 x 7 with 205 tyres on my 7, handling and tram lining was awful
there now 13x6, 185/55 and its like driving a different car,
JMHO
steve
Thats was probably spelt wrong, or had some grammer, that the "grammer police have to have a moan at
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Dick
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| posted on 16/2/15 at 04:50 PM |
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Ash that had the saab with a hb turbo used to run 195 70 15 on his and never had a problem think he was on 7 or 7 1/2 rims he all ways seemed to be
able to put the power down
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Dan.
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| posted on 16/2/15 at 04:54 PM |
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quote:
Originally posted by Dick
Ash that had the saab with a hb turbo used to run 195 70 15 on his and never had a problem think he was on 7 or 7 1/2 rims he all ways seemed to be
able to put the power down
guessing he didn't have over 400hp with very little lag? Even with big tyres I'm not expecting it to put the power down well but want to
give it a fighting chance.
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Dick
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| posted on 16/2/15 at 04:57 PM |
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Oh im sure he will be along soon to tell you different , wide tyres give low ground pressure so you can end up going backwards in grip if they are to
wide
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steve m
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| posted on 16/2/15 at 06:20 PM |
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ive been in ash car, bloody quick !
Thats was probably spelt wrong, or had some grammer, that the "grammer police have to have a moan at
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steve m
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| posted on 16/2/15 at 06:23 PM |
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If still doubting ask Hicost, as he had 400bhp + and then nitrous, 650 at the wheels I believe
another car ive been in, and warp speed quick !
Thats was probably spelt wrong, or had some grammer, that the "grammer police have to have a moan at
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Dan.
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| posted on 17/2/15 at 12:33 PM |
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Have spoken to hicost
He uses 265 x 40 x 15 on the rear and 235 on the front or 225 on the fronts and 245 on the rear.
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Pat_T
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| posted on 17/2/15 at 01:04 PM |
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No!
Whatever you do don't put that much tyre on the front you'll ruin it.
Even the Caterham 620R runs 185 fronts!!
I had 200+ bhp at the wheels and I changed from 195 front to 185 front and it improved the car no end.
Anything above 205 on the front is going to make it tramline like crazy and you will lose a lot of steering feel. If you do trackdays you will also
really struggle to get heat into the fronts with a tyre that wide.
I ran 205 rears, I imagine 225 rears will be plenty for upto 350bhp...
www.instagram.com/patroclueus
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Dan.
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| posted on 17/2/15 at 02:00 PM |
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quote:
Originally posted by Pat_T
No!
Whatever you do don't put that much tyre on the front you'll ruin it.
Even the Caterham 620R runs 185 fronts!!
I had 200+ bhp at the wheels and I changed from 195 front to 185 front and it improved the car no end.
Anything above 205 on the front is going to make it tramline like crazy and you will lose a lot of steering feel. If you do trackdays you will also
really struggle to get heat into the fronts with a tyre that wide.
I ran 205 rears, I imagine 225 rears will be plenty for upto 350bhp...
The 620R is a pussy cat compared to hicosts / my seven, I am expecting between 400 and 450bhp and oodles of torque.
I will have to suck it and see, I just dont want to invest big money into rims if they are not going to compliment the car, I have some 7.5J ET35
wheels I can put on the front and a friend has a set of 8.25J wheels I can put on the rear for testing and see how I get on.
As always many conflicting opinions...
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JAG
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| posted on 17/2/15 at 02:26 PM |
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When you're doing something different there's always an element of suck-it-and-see I'm afraid 
You may well go through a few wheel and tyre options until you get one you like.
Justin
Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!
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jeffw
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| posted on 17/2/15 at 02:41 PM |
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I drive a 'pussy' cat car with 400BHP/300 ft lb and run 185/60 13 front and 215/50 13 rear...7J front and 8J rear wheels. With all your
extra power I'm surprised your 'mans' car doesn't need 22" rims and spinners or something lol...
[Edited on 17/2/15 by jeffw]
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Dan.
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| posted on 17/2/15 at 03:00 PM |
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quote:
Originally posted by jeffw
I drive a 'pussy' cat car with 400BHP/300 ft lb and run 185/60 13 front and 215/50 13 rear...7J front and 8J rear wheels. With all your
extra power I'm surprised your 'mans' car doesn't need 22" rims and spinners or something lol...
[Edited on 17/2/15 by jeffw]
Wasnt trying to insult anyones car... My point is the 620R 310 BHP // 219 LBS is a substantially different beast to 450 BHP // 350 LBS.
The only reason i dont want 13s is because they will not fit over my brakes... the question was around width and offset specifically.
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rodgling
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| posted on 17/2/15 at 04:37 PM |
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I'm running 205 15" at the front and 225 15" at the rear. IIRC rears are 7J, fronts are 6.5J. This seems to work well with 320
bhp/260 ft-lbs, no problems putting the power down. Although possibly the fronts would benefit from being a bit narrower for better feel.
8.25J sounds too wide to me.
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beaver34
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| posted on 18/2/15 at 07:45 AM |
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in on 205 rear 185 front 13" @ 340bhp on a r888, its fine in regards to straight line grip
not sure what your building the car to do but i use mine on the road and its fairly pointless and was better with less power
just my experience 
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Dick
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| posted on 18/2/15 at 09:20 AM |
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Im going to ask as im sure others are all waiting to find out like me ,
What engine are you using and what have you done to it to give 450 with very low lag ? The reason behind the question is I have a very good Saab
engine sitting in my workshop and was thinking about what to do with it and what to fit it in . I have had lots of people tell me its easy to get
power out of these engines but opinions all seem to differ
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Dan.
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| posted on 18/2/15 at 11:25 AM |
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quote:
Originally posted by Dick
Im going to ask as im sure others are all waiting to find out like me ,
What engine are you using and what have you done to it to give 450 with very low lag ? The reason behind the question is I have a very good Saab
engine sitting in my workshop and was thinking about what to do with it and what to fit it in . I have had lots of people tell me its easy to get
power out of these engines but opinions all seem to differ
Engine is a Saab B204 lump, when installed in my daily drive I fitted a holset, some 630 injectors and 3 Bar MAP resulting in ~450HP unfortunatly it
didnt come on song till 4500RPM when all hell broke loose, not ideal for the kit car but very simple and resulted in lots of power for minimal cost.
Spool could have ben improved with a better manifold, Cams and a shot of nitrus.
I decided I'd take a different approach... (I will do a thread at some point)
I have 2 designs I am going to test, the first and lightest design will use 2 x stock saab turbos, all exhaust gass will flow through one turbo untill
it has spooled up to X PSI, at this point the 2nd turbo will be introduced and work in parallel. This is purely a mechanical solution and relied on a
reed valve, butterfly valve, external wastegaste and a couple of actuators for the internal gates. I have built it but am yet to test, im confident it
will spool nice and early but am concerned it may choke up at the top end.
The second solution will use the big Holset attached to the manifold and a small turbo down stream the exhaust gas will flow through the holset and
when unspooled will be bypassed into the standard Saab turbo, however once the big turbo begins to spool the small turbo will be completly bypassed. I
am more confident this design will work though it wont spool as early as the above setup but it will not choke up at higher flow like the other design
might. Again purely a mechanical solution I am not confident enough to experiment with electronic control at this point... in the future who knows!
It is a case of suck it and see, it is the most experimental bit of my car hopefully it works out, if not there are plenty of other options I can try
such as a VGT or just big turbo and nitrus etc.
[Edited on 18/2/15 by Dan.]
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Dan.
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| posted on 18/2/15 at 11:30 AM |
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quote:
Originally posted by beaver34
in on 205 rear 185 front 13" @ 340bhp on a r888, its fine in regards to straight line grip
not sure what your building the car to do but i use mine on the road and its fairly pointless and was better with less power
just my experience
I'm building it because I can... not the best of reason but good enough for me
Ive read many times its too much power etc etc, at the end of the day it isn't a race car trying to be competitive its a track day toy to have
fun in and I'm sure it will be fun.... even if a little terrifying
[Edited on 18/2/15 by Dan.]
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beaver34
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| posted on 19/2/15 at 09:09 AM |
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quote:
Originally posted by Dan.
quote:
Originally posted by beaver34
in on 205 rear 185 front 13" @ 340bhp on a r888, its fine in regards to straight line grip
not sure what your building the car to do but i use mine on the road and its fairly pointless and was better with less power
just my experience
I'm building it because I can... not the best of reason but good enough for me
Ive read many times its too much power etc etc, at the end of the day it isn't a race car trying to be competitive its a track day toy to have
fun in and I'm sure it will be fun.... even if a little terrifying
[Edited on 18/2/15 by Dan.]
the same reason i built mine
sure will be fun
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theduck
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| posted on 19/2/15 at 01:36 PM |
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Is there any better reason to build a car?
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jwhatley
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| posted on 19/2/15 at 04:45 PM |
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Having had all the big pub numbers in my last MK, i have to ask what brakes you are using to suggest you can't use 13's? How heavy do you
expect the car to be?
If the car is going to be above, say 750kg wet with driver then I'd say it would start to encroach on having bigger brakes, however if it is
not, you will not get the heat in the brakes. Especially if you are keeping it road legal, which I suspect you are.
Do not go above a 7.5 on the front or a 205 tyre, again if you do, then the car will actually handle badly and you will get barely any heat in the
tyres unless you run considerable toe in.
On the rear, I had a 9in on et20 with MK wide arches (this was an R chassis) and a 245 rear, and equivalent slick. Any more and you would probably
start to loose effective grip (or not gain any more) due to the loading over the area, without having to look at adjusting pressures, which changes
handling characteristics.
It's all very well having this power and torque, but let's face it's going to be un-usable. I speak from experience when I say
it's best to loose say 40bhp when mapping for a chance to have a smooth, usable and linear power curve, this is what I did and it made a world
of difference.
At 586kg wet with driver and 414bhp/262ftlb at the rear wheels. I will happily say I'll never get in something that could accelerate as quickly
again. Sometimes I wish I didn't sell it, but I realised that if I kept it road legal I'd either die or loose my license. Hence why the
new car is track only.
There's nothing better than experience, after all that's what building it will give you. You can only make it better by learning from
experience.
Good luck I say, don't listen to the haters and enjoy your build!
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Dan.
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| posted on 19/2/15 at 05:24 PM |
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quote:
Originally posted by jwhatley
Having had all the big pub numbers in my last MK, i have to ask what brakes you are using to suggest you can't use 13's? How heavy do you
expect the car to be?
If the car is going to be above, say 750kg wet with driver then I'd say it would start to encroach on having bigger brakes, however if it is
not, you will not get the heat in the brakes. Especially if you are keeping it road legal, which I suspect you are.
Do not go above a 7.5 on the front or a 205 tyre, again if you do, then the car will actually handle badly and you will get barely any heat in the
tyres unless you run considerable toe in.
On the rear, I had a 9in on et20 with MK wide arches (this was an R chassis) and a 245 rear, and equivalent slick. Any more and you would probably
start to loose effective grip (or not gain any more) due to the loading over the area, without having to look at adjusting pressures, which changes
handling characteristics.
It's all very well having this power and torque, but let's face it's going to be un-usable. I speak from experience when I say
it's best to loose say 40bhp when mapping for a chance to have a smooth, usable and linear power curve, this is what I did and it made a world
of difference.
At 586kg wet with driver and 414bhp/262ftlb at the rear wheels. I will happily say I'll never get in something that could accelerate as quickly
again. Sometimes I wish I didn't sell it, but I realised that if I kept it road legal I'd either die or loose my license. Hence why the
new car is track only.
There's nothing better than experience, after all that's what building it will give you. You can only make it better by learning from
experience.
Good luck I say, don't listen to the haters and enjoy your build!
Thanks for the feedback it is much appreciated from someone who has had a similar car, though yours was busa powered wasnt it?
In answer to your questions:
Im hoping the car will be under 600KG's but this remains to be seen once built up, it isn't having any niceties however does have a cage
and other chassis reenforcement and is a CEC all of which will push the weight up, so may well be over this target figure.
Current Brakes are cosworth items the car 'started' off as more of a budget build and wilwoods were out of the question, that however may
change as the cosworth brakes would serve well as boat anchors, if so this will open up the option for 13s, I want to try the current setup before
outlaying too much more cash as I may well be happy with it... but obviously 13s would be preffered.
Car will be a mixtrure of road and track, as with you I may well invest in some slicks too.
Mapping is something I will be able to adjust at the touch of a button, I will have access to numerous maps and be able to tweek the maps on the fly
which is something I look forward to playing with, like you say the biggest power may not (probably wont) be the best option for performance in the
real world.
Regarding tyres what brands are available who provide such wide 15/13s?
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jwhatley
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| posted on 19/2/15 at 06:35 PM |
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Yes it was busa powered.
Try Avon - look at the CR500 in perticular. Great all round track day/road tyre.
Under 600kg for you wet with driver I doubt will be achievable to be honest, especially if you are charge cooling and dry sumping.
I had adjustable boost with waste gate and spool up correction against RPm. It was the closest I could get to launch control as my Ecu didn't
support it. I had just the one map which used boost/rpm/temperature compensation against MAP/TPS. That way I could control the boost through my
controller and have the engine map correct for each boost setting.
Personally, I'd ditch the cosworth ones and sell them. You'll be surprised how much they will fetch compared to say a willwood setup. Plus
you are talking a huge amount less unsprung weight.
TBH - It's all very well having the power and the go, but when you can't corner or stop then you really are wasting your time building the
car to be 'quick'.
[Edited on 19/2/15 by jwhatley]
[Edited on 19/2/15 by jwhatley]
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