Tyre fitment help...

[Boris396]

Morning guys and girls

I'm in the middle of ordering a new set of wheels and tyres for the Nova - Cragar 344s and BFG Radials.

The wheels I'm looking at are:
Front - 15' x 8'
Rear - 15' x 10'

By my maths that would mean the tyres need to be:

Front - 205/60/15
Rear - 255/60/15

But a little digging on the net when trying to find PCD fitment for my year Nova has taken me on a various forums in which people seem to be talking about running 265+ tyres on as little as 8' wide wheels, which struck me as strange. Surely you would have bulging side walls and an accident waiting to happen?

Anyone clear this up for me or at least confirm or refute my maths?

 

[TransAmDan]

I'm running 275 at the back on an 11 inch rim. so I guess an 10 inch rim would be about 20mm narrower, So a 255 would be about right. You could get away with 265.

On my old Firebird, it was meant to have 215's at the back, I popped on 235's on the standard rims and it didn't look wrong. Nothing bulging out. I think 20mm +/- of the ideal one for the rim is okay, I wouldn't want to go much further than that though.

265 tyres on an 8 inch rim surly cant look right. The flat part of the tyre that contacts the ground would be going curved. If anything you would probably have less grip when getting up to speed as only the center of the tyre would touch the ground.

 

[AmericanThunder]

Dan, Most of the US boys running an 11" rim are running tyres bigger than 275. On that size rim they would normally fit a 315.
I was running 275 on 9.5" rims and the look was perfect - no bulging sidewalls etc but then I based my choices off the standard Firehawk size which was 275 on 9" rims. Of course these are 17" diameter wheels.
Not saying your wrong - just an observation.

 

[TransAmDan]

oh no, perhaps you are right. I've never measured the actual rim, it may only be a 10inch. Or maybe is 9inch like the Firehawk. I'm gonna have to measure now, lol.

 

[AmericanThunder]

I'm far from an expert on tyres but I do remember running oversize tyres on my 2nd gen f-body
Stock size was (IIRC) 225/60 * 15 on 7" rims
I ran 235/60/ * 15 on the same 7" rim front and 255/50 * 15 on the same 7" rim on the rear.

This gave it a nicely filled out look without stupid looking bulging sidewalls. The decrease in profile vs the wider contact patch minimised the overall tyre height.
Tyre height is also worth remembering or your speedo will read wrong.

I found a nice visual web site here: Visual Tyre Size Calculator | Kouki Tech
and a tyre height calculator here: Tire Height Calculator - Wallace Racing

You could input your stock size and then play around with other sizes keeping the overall tyre height very close and check out the visual representation as well.

Hope that helps.

 

[saleen 192]

These people might help?
Vintage tyre,classic and American tyres North Hants Tyres.
have used them had good service

 

[Rob63]

Hi I have 15 x 10 rims fitted with 265 at front and 295 on rear they havn't fallen off so must be a fairly good fit
Oh and must remember speedo reading is + 10%

 

[renchero]

putting a wider tyre on a wheel might look ok but allows the wheel to roll sideways within the tyre making the car roll around more when going around corners. when i put new wheels and tyres on the ranchero i kept the same size tyre 235 but changed from a 7" to a 8" rim,the back end is now a lot more stable

 

[AmericanThunder]

putting a wider tyre on a wheel might look ok but allows the wheel to roll sideways within the tyre making the car roll around more when going around corners. when i put new wheels and tyres on the ranchero i kept the same size tyre 235 but changed from a 7" to a 8" rim,the back end is now a lot more stable

Yes, agreed. But at what point is a tyre to wide for a rim?
The original poster was thinking 205/60 * 15 on an 8" rim front and 255/60 * 15 on a 10" rim.
I think both of these are too small considering OE sizes. For example, 93-97 Firebirds came with a 255/50 * 16 on an 8" rim, 98-01 Firehawks came with 275/45 * 17 on a 9" rim.
My Z06 has 265/40 *17 on a 9.5" rim front and 295/35 * 18 on a 10.5" rim rear.
The ability of the wheel to roll around with an oversized tyre is limited by tyre height. Maintaining tyre height by lowering the profile relative to the cross section allows you to run a wider tyre without the roll, up to a point of course.
For example, using my car as an example, the stock sizes are great for the road but those seriously into handling change to a square setup (using the same size on all four corners). It's quite common to use the rear wheels on the front, with 305/30 on all four corners. Typically this is done with larger sway bars that would only increase roll from the tyres. The racers would not do this if the effect on handling was negative. One of the major benefit for them would be the ability to turn into a corner faster before under steer becomes an issue.
So at what point is a tyre too wide for the rim? Not sure, you probably only find out through experimentation but given the OE sizes used on a given rim width, I would suggest that none of the tyres mentioned so far are too wide for their intended purpose.

 

[Boris396]

Cheers for the responses guys.

I got it all a bit wrong. I was initially under the impression that the tyre size had to match the wheel size (10inch = more or less 255mm)

I've checked my current wheels and tyres, I'm running 9.5" rears with 255 tyres and 8" fronts with 235 tyres.

Having checked with the tape measure I'm pretty much at the limit of width at the rear without modifying the spring position or tubbing it.

Someone showed me this site which has come in handy..
Tyre equivalence: Car tyre tips - Pneus Online

Due to limited sizing with the wheels I want and based on what the above site states I'm gonna go with:

15x8 rears with 235 or 245 tyres
15x7 fronts with 205 or 215 tyres

My new issue is to a opt for the Hercules HP4000 tyre or BFGs. The HP4000s are a fair bit cheaper. Any body had experience with both?

Any yeah I'll be getting it all through North Hants

 

[TransAmDan]

I've not tried the HP4000's, I have run BF Goodrich though, they smell sweeter on a burnout . I ran them for a number of years, the wear was good, and good grip in the dry. Had to take a bit of care in the wet, but they were no worse than other tyres I tried on the reat like Falken's.

 

[AmericanThunder]

Hope I was able to help.
Based on your rim sizes I would go with the 245 on the rear and the 215 on the front.

 

[Boris396]

Hope I was able to help.
Based on your rim sizes I would go with the 245 on the rear and the 215 on the front.

Very much so mate, much appreciated.

My thoughts too, I'.m just waiting on a price now.

 

[Boris396]

I've not tried the HP4000's, I have run BF Goodrich though, they smell sweeter on a burnout . I ran them for a number of years, the wear was good, and good grip in the dry. Had to take a bit of care in the wet, but they were no worse than other tyres I tried on the reat like Falken's.

Well I wont be doing many burnouts with while I've still got this open diff! Converting to a posi is high on my list of priorities.

I'm booked in at Bob Harman in 3 weeks for a tune up so am gonna pop in to the axle shop next door and have a word.

I'll probably go for the HP4000s to be honest. They a good ?20+ a tyre cheaper.