Slower due to alloys?

[Alan16ac]

Could 18" RS6's on my 1.4 golf mk4 cause it to be slower?

[macmillions]

Yes.

My mate put 17's on his Felicia and it topped out at 85mph, whereas before it could hit a ton. (on a track of course...) :biglaugh:

[onzarob]

do you know how much heavier 18in alloys are compared to your standard wheels? Well it allot. Big Tyres grip the road more = more resistance = harder work for the engine :(

[Alan16ac]

All I can say is my alloys are a lot lighter, I have picked both wheels up you can feel a slight weight difference, but it is an awful lot slower, gone from 14" to 18" and maxes out at 85 and HATES hills, but they look nice so I'll put up with it, I'm only 17 so more power isn't an option, and sure on a track of course ;).

[onzarob]

its also the amount of rubber on the road = more friction. yep its a trade of looks versus suitability.

[Alan16ac]

Yeah I guess, okay thanks. :)

[scotty33]

You should bear in mind that the rolling radius/circumference of the new tyres is probably a lot larger now. Whatever the percentage change is, the speedo will be under-reading by that amount.
Has probably upset the gearing too, car probably no longer has the power to reach peak revs.
Another effect is the brakes are probably working harder, the extra diameter increases the braking torque, basically more pedal pressure is needed to achieve the same stopping power - though you should have more grip available

[Alan16ac]

The speedo has been calibrated for my new alloys :).
And yeah ah well they look phiiit

[xenon]

You should bear in mind that the rolling radius/circumference of the new tyres is probably a lot larger now. Whatever the percentage change is, the speedo will be under-reading by that amount.
Has probably upset the gearing too, car probably no longer has the power to reach peak revs.
Another effect is the brakes are probably working harder, the extra diameter increases the braking torque, basically more pedal pressure is needed to achieve the same stopping power - though you should have more grip available
There should be no change in diameter of the tyre or there will be problem, not least with the tyres potentially fouling the bodywork (unless the bodywork has been modified too). The main problem, as already mentioned is the speedo reading wrong - I didn't think it was possible to calibrate a speedo to compensate for different diameter wheels. The usual rule is to keep the change in diameter when upsizing the rims as small as possible (+/- 2.5% I think).

Alan16ac - what size tyres have you gone from, and what are you running now?

[Alan16ac]

I really don't know that much, not sure what they were before. But I have 18" with 35mm Tires? Does that makes sense lol.

[xenon]

I really don't know that much, not sure what they were before. But I have 18" with 35mm Tires? Does that makes sense lol.
I understand the 18" bit but that's all! The '35' may refer to the profile of the tyre. i.e. the height of the tyre profile is 35% of the tyre width. Easily checked by looking at the sidewall of the tyre which should read something like 255/35R18 where the 255 is the tyre width (mm), 35 the tyre profile ratio and 18 being the rim size (in). I've no idea why they mix milimeteres and inches!

BTW 255/35R18 would be the correct size for your car.

[scotty33]

Alan

you should be able to get the oiginal tyre size from the handbook?

Just put in the numbers from the old and new tyres here :



http://www.tacomaworld.com/forum/tirecalc.php

Should give you some idea.

[Hurdy]

I understand the 18" bit but that's all! The '35' may refer to the profile of the tyre. i.e. the height of the tyre profile is 35% of the tyre width. Easily checked by looking at the sidewall of the tyre which should read something like 255/35R18 where the 255 is the tyre width (mm), 35 the tyre profile ratio and 18 being the rim size (in). I've no idea why they mix milimeteres and inches!

BTW 255/35R18 would be the correct size for your car.

Sorry, but this is wrong. The stock tyre size for a MKIV should be 225/40/18

If you are running on 35 profile tyres then the difference to stock size means the wheels have to turn 3.5% faster to get the same speed as you would have if you had chosen the correct tyres.

Add to this the fact that each tyre has a 15% larger footprint than before (which generates more rolling resistance) and you can begin to see where you are losing your top speed capability.

You will also see a lower MPG too.

[Cheap Car Tyres]

I always thought that alloys only ever affected the handling of the vehicle in my experience. Though it may be the case that it is slowing down your car depending on the weight of the allows and the weight of the car.

Brian

[Sam]

The speedo has been calibrated for my new alloys :).
And yeah ah well they look phiiit

Your speedo was calibrated for the new wheels?

How was this done?

[Hex69]

Your speedo was calibrated for the new wheels?

How was this done? Tippex or stickers :D

http://www.eastcoastimport.co.uk/speedo%20jpg.jpg

[Eshrules]

you took the lowest ever powered golf, the 1.4 and you put whopping great 18 inch wheels on it, increasing weight and friction.

of course it'll be slower ;) I'd also be concerned about the stress placed on the diff/gearbox as a result.

[Alan16ac]

Don't try and make me look stupid lol.
Are you gonna pay for the insurance on a 1.6 or bigger?
I'd love to have a more powerful golf, but the insurance is costing more than the car already. (I'm 17 btw).

[Eshrules]

Don't try and make me look stupid lol.
Are you gonna pay for the insurance on a 1.6 or bigger?
I'd love to have a more powerful golf, but the insurance is costing more than the car already. (I'm 17 btw).

i'm only 24 myself, insuring a group 13 audi avant, so you don't need to explain to me the cost of insurance.... I'm not sure how I made you look stupid, that wasn't my intention, apologies.

In regards to your insurance, if you remove the wheels and actually use the stock rims, your insurance will plummet.

[Sam]

I still would like to know how you had your speedo calibrated :)

[Alan16ac]

Yeah, but I like my alloys. I put up with it being a wee bit slower.
And I don't know my cousin did it. He works for Audi/VW. I'll ask him if you want next time I speak to him. Either way The speed of my car matches that on the dashboard, I've tested with my SatNav.

[Sam]

Ahh, then you probably upsized your wheels but downsized your tyres.

If your SatNav speed exactly matches your speedo - you're fine and it's the weight of the wheels coupled with the increased "footprint" that's slowing you down.

[onzarob]

Yeah, but I like my alloys. I put up with it being a wee bit slower.

That the most important thing, not what us lot think, Its your car enjoy...your right thought it look nice :)

[scotty33]

It could still be that the speedo is reading slower than it used to at the same speed. I say this because most cars speedo's read approx 5-10% too fast. If yours matches the sat nav (which is accurate) then it is reading slower than it would normally.

If the car is slower on the sat nav since the wheels were fitted, it must be a combination of gearing/friction etc as outlined above?
I would say it is worth getting your tracking checked/reset, if this is slightly out the drag it causes is exaggerated by wider tyres, and you would not want to wear out the new 18's before their time?!!

[Alan16ac]

Can't remember who asked, but I checked today, they are 225/40/18

[xenon]

Can't remember who asked, but I checked today, they are 225/40/18
It was me! That tyre size works out 1mm bigger in diameter than the standard fit wheels on your car. Shouldn't have needed to adjust anything as the wear on tyres can make a difference of about 10mm in diameter.

[Bobster-cyw]

I still would like to know how you had your speedo calibrated :)


Not sure about for a golf specifically but I've had speedo's recalibrated in the past by speedcables.co.uk. They can either recalibrate by adding something to the cable (for mechanical driven speedos) or can recalibrate the actual unit.

I had mine done for a classic vw because I fitted different size wheels and tyres and the original unit was giving incorrect readings, I just had to take some simple measurements based on the size of the wheel, distance travelled in one rotation etc etc and they did the rest.