Tyre options

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ZedRS6
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Tyre options

Post by ZedRS6 » Thu Jan 03, 2019 11:01 pm

Hi folks
Need some help in choosing tyre size

Currently I have 20” 9j ET35 sportec wheels fitted with 255/30/20 tyres.

I wanted to go for a bigger profile tyre as I find the 30 profile is too thin and I feel every thing on the road.
Now I wanted to go up one profile to a 35, would I need to change the width size too? Or am I ok with just having a bigger profile on the 255 fitment.

Thanks in advanced

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Shoppinit
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Re: Tyre options

Post by Shoppinit » Thu Jan 03, 2019 11:16 pm

You could probably put a 235/35/20 on. This would increase your rolling radius by about 2%. Might look odd though.

If you’re on H&R suspension this is probably the cause of the bone shaking.
Daytona RS6 C5 Avant. Viper'd, Billies, Waggers, MTM box brain, C6 stoppers, xcarlink, R8 coolant cap (woohoo)
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ZedRS6
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Re: Tyre options

Post by ZedRS6 » Thu Jan 03, 2019 11:21 pm

Shoppinit wrote:
Thu Jan 03, 2019 11:16 pm
You could probably put a 235/35/20 on. This would increase your rolling radius by about 2%. Might look odd though.

If you’re on H&R suspension this is probably the cause of the bone shaking.
235?? Would I have to go that narrow to fit a 35 profile??
It’s on bilsteins atm I haven’t had a chance to see what the damper settings are on but it does seem quite firm with hardly any recoil.im sure I’ve had it bottom out on a speed bump that I approached abit too quickly.
03 Audi RS6 Avant with Sportec upgrade.
00 Audi S4 B5 Avant-Sold with regrets
97 Honda Civic Type R EK9- K20'd -current project
99 Audi 1.8TQS Avant -Sold
99 Subaru Impreza STI V5 -Sold still miss it
02 VW Golf V5 MK4 -Sold
95 VW Corrado VR6 -Sold
96 VW Polo 1.0 -Sold
97 Honda Civic Vti EK4 - Sold

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Shoppinit
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Re: Tyre options

Post by Shoppinit » Thu Jan 03, 2019 11:30 pm

Yeah, they bottom out easily but they are otherwise quite comfortable if they are set on 4.

If you go 255/35 then your rolling radius will increase by 4%. That’s starting to be quite a lot.
Daytona RS6 C5 Avant. Viper'd, Billies, Waggers, MTM box brain, C6 stoppers, xcarlink, R8 coolant cap (woohoo)
///M3 E46 | XC90 (V8, natch) | Passat GTE | RR Classic V8 flapper
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."

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Daveperc
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Re: Tyre options

Post by Daveperc » Fri Jan 04, 2019 10:43 am

I don't quite understand this conversation!

If you are trying to increase the depth of the sidewall of the tyre to get something more compliant then for any given wheel size you will increase the rolling radius. If you want deeper sidewalls you have to fit smaller wheels (19") if you want to keep the rolling radius the same.

The Mich PS4S have a fairly compliant sidewall.

ZedRS6
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Re: Tyre options

Post by ZedRS6 » Fri Jan 04, 2019 1:45 pm

Daveperc wrote:
Fri Jan 04, 2019 10:43 am
I don't quite understand this conversation!

If you are trying to increase the depth of the sidewall of the tyre to get something more compliant then for any given wheel size you will increase the rolling radius. If you want deeper sidewalls you have to fit smaller wheels (19") if you want to keep the rolling radius the same.

The Mich PS4S have a fairly compliant sidewall.
I wanted to know if I I can increase the depth of the sidew to a 35 profile and keep the same 255 width.
03 Audi RS6 Avant with Sportec upgrade.
00 Audi S4 B5 Avant-Sold with regrets
97 Honda Civic Type R EK9- K20'd -current project
99 Audi 1.8TQS Avant -Sold
99 Subaru Impreza STI V5 -Sold still miss it
02 VW Golf V5 MK4 -Sold
95 VW Corrado VR6 -Sold
96 VW Polo 1.0 -Sold
97 Honda Civic Vti EK4 - Sold

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Daveperc
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Re: Tyre options

Post by Daveperc » Fri Jan 04, 2019 3:07 pm

Hi - yes I understood the question, but not the subsequent conversation.

There are two issues with increasing to 35 profile: physical space, and rolling radius. Remember the "35" is a percentage of the width (255).

There probably is physical space, though you will be pushing the inner corner of the front tyres very close to the protuberance known as "Ol' Knobbly". It will almost certainly need to be ground off, and even then with some makes of tyre you may have a problem - it will depend on how square the section of the tyre is.

On any tyre the rolling radius will be increased (by about 4%) which means that your indicated speed on the speedo will be under reporting by 4% (ie roughly 3MPH at 70. It also means that you will be under reporting the distance covered by the car. I'm not aware if there are specific regulations on how far out you are allowed to be, but you will certainly need to be careful near cameras etc.

Most advice is that you keep the rolling radius as close to the OEM spec as you can - hence my comments.

Hope that helps

Dave

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