not sure where to start ,I had my vrs in to a dealer for a small cosmetic repair.The dealer loaned me there vrs tdi in the mean time while mine was being sort after,I don't know if it was just me but the dealers vrs felt a bit quicker than mine.The only difference between the two was a difference of about 1000mile on the clock and that mine had 18" rims as where the dealer had 17"inch would that make a difference?Im thinking as the dealers was a demo car they hammered it from the get go, would it make a difference?I was sad to give the demo car back as I thought mine was not as fast as this one .You would expect the cars to feel identical as they having exactly the same engines weird:confused:

There will always be slight variances withn any particular model - there will be some good ones, and some not so good ones.

Other factors such as the number of miles covered and the type of fuel will also affect performance.

I was just going to suggest fuel - SWMBO's car was low on derv on Friday and given the limitations of the company fuel card we had to put Morrisons fuel in. We have noticed before with this fuel in the other car she'd had recently that the PD140 really doesn't seem to like something about it. I would thnk the 170 would be similar.

I would imagine that each engine will come witth slightly different powers. Some may have 165 others may get to 175bhp. Also I would think that 17's would make it accelerate quicker. Giving the illusion of a faster car, would probably feel the same with 18's on.

The tyre size will make no difference.

If different wheels had different rolling radii then the speedometer and mileometer would be out if a manufacturer offered wheel choices. It would also imply that the manufacturer would have to make a different final drive gear ratio for every wheel size offered:eek:

The wheel size is compensated by taller or shorter side walls.

The vRS 17s have 225/45s and the 18s have 225/40s

The second number after the "/" is the tyre wall ratio as a percentage of tread width.

The 17s have an overall tyre diameter of 634 mm and the 18s have OD of 637mm.

So yes, technically, the same car on 17s would have a 0.47% advantage in a sprint (assuming sidewall flex is not detrimental). That would be an imperceptable 4/100s of a sec to 62mph.

This 3mm discrepancy is also irrelevant as the tyre itself has a wear error of up to 16mm (8 mm of tread each side) assuming you ran it to bald or 12.8mm if you ran to legal minimum.

If you want to check size comparisons, have a play with this size calculator:

Changing tyres sizes - tyre size change calculator

doh, forgot to account for the taller side wall. Sleep needed.

......was the dealer's car chipped?

But the 18" alloys will make for a greater unsprung mass and so slower acclelation compared to the 17" tyres.

Air filter, fuel, fuel filter and if your car is just due for a service can all make the car a bit slower.

I was just going to suggest fuel - SWMBO's car was low on derv on Friday and given the limitations of the company fuel card we had to put Morrisons fuel in. We have noticed before with this fuel in the other car she'd had recently that the PD140 really doesn't seem to like something about it. I would thnk the 170 would be similar.

I carry a bottle of millers cetane booster around for just that kind of situation

Chris

But the 18" alloys will make for a greater unsprung mass and so slower acclelation compared to the 17" tyres.

Air filter, fuel, fuel filter and if your car is just due for a service can all make the car a bit slower.

How much extra do they weigh?

Can't think is is more than a few kgs per corner (what with slightly smaller tyre aswell)

How much extra do they weigh?

Can't think is is more than a few kgs per corner (what with slightly smaller tyre aswell)

2.5kg per wheel tyre!

17" Pegasus with 225/45s vs. 18" B14s with 225/40s. Wheels are 2kg heavier & tyres 0.5kg heavier (for the 18s).

I have weighed both sets wheels/tyres separately and IMHO the car does feel a smidgen sharpen on the 17s.

Overall though fuel etc will also have a lot to do with performance.

Maybe someone at the dealers put Shell V-Power diesel in it?

When mine went in for a service the dealer lent me their new vRS diesel demonstrator and although I didn't think there was any difference in performance, it did ride a bit more comfortably on the 17" wheels.

It's the heavier wheels, unsprung mass will kill your performance. 10 kg is a lot, you definitely can feel it if that is added to the wheels.

Also, I bet that the dealers car has been booted a lot. It will open up the engine.

Was the dealers car equiped with the new CRD engine?

Was the dealers car equiped with the new CRD engine?

Are there any NEW engines in the UK yet ?

I would think end of June begininig of July for new CRs.

They went into production week 22 AFAIK. This is end of May. So with delivery times of 2 to 3 weeks they should be here by the end of this month. But dealers wont necessarily put a new 170CR on as demo if they still have a fresh 170PD on the books.

It's the heavier wheels, unsprung mass will kill your performance. 10 kg is a lot, you definitely can feel it if that is added to the wheels.

:confused: you 'might' feel a difference in turn in but that could be the different profile tyres just as much as the unsprung weight - 10kgs wouldn't make much if any difference to acceleration on a 1500kgs car (that's only 0.65% increase) just buying a bag of shopping on the way home could increase the overall weight by that much

:confused: you 'might' feel a difference in turn in but that could be the different profile tyres just as much as the unsprung weight - 10kgs wouldn't make much if any difference to acceleration on a 1500kgs car (that's only 0.65% increase) just buying a bag of shopping on the way home could increase the overall weight by that much

Its not the extra weight per se; its the fact that it is a 'rotational mass' that has a proportionally greater 'apparent weight' than actual weight. (my physics is not so hot theses days so I can't tell you how much).

Could just be normal variation.

Not quite in the same league as your VRs but a few years ago my company had 2 pool cars - both Peugeot 405 (or was it 406?) 1.9 turbo diesels, identical spec except 1 was a saloon and 1 was an estate; both were typically abused pool cars from new, both were fuelled at the local Shell station, both were serviced to the book at the local Peugeot dealership.

I drove both regularly and the estate always out-performed the saloon - it always felt much more responsive. On one particular hill, the estate would climb it easily at 75mph, the saloon struggled to reach 70.

At the time I had a Xantia with the same engine - it was better than the saloon but nowhere near as good as the estate.

Are there any NEW engines in the UK yet ?

Dunno - hence the question mark

:confused: you 'might' feel a difference in turn in but that could be the different profile tyres just as much as the unsprung weight - 10kgs wouldn't make much if any difference to acceleration on a 1500kgs car (that's only 0.65% increase) just buying a bag of shopping on the way home could increase the overall weight by that much

Unsprung mass if a different story. I'm not that good in mathematics, so I can't provide you a formula that shows the effect. However, I've been told by racing guys that 1kg extra of unsprung rotational mass has just about the same effect as 10kg weight added to the car. So, 10kg extra on the wheels would have the same effect as if you would take a 100kg friend to sit in the car. Lightweight flywheel, anyone? It is a good example of the effect how rotational mass makes a difference.

There is a very good reason for why they have these superlight wheels when racing.

"US magazine Sport Compact Car found some of these effects when their late model Honda Civic was fitted with an upgraded wheel/tyre package. The starting point was a set of 185/65 Dunlops on 14 inch steel wheels. Each wheel/tyre weighed 15.5kg. They then went to 205/40 Nitto tyres on 17 inch alloys, which increased each corner's mass to 19.5kg. This 4kg (26 per cent) per wheel increase in mass was enough to drop the power measured at the wheels on a Dynojet chassis dyno by nearly 5 per cent! This means that even a kilogram added to the rotating assembly is important - each kilogram that was added to the Civic's individual wheel/tyre mass decreased power at the wheels by over 1 per cent."

Autospeed - Heavy action

"The use of light-weight alloys in wheels reduces rotational mass. This means that less energy will be required to accelerate the wheel. Given that each pound of rotational mass lost provides an equivalent performance gain as a 10 pound reduction in vehicle weight, the benefits of light alloy wheels on vehicle performance cannot be overlooked.

For example:

A reduction in the weight of the rim/tire assembly of 5lbs x 4 (all around the car) is equivalent to a 200lb weight reduction in vehicle weight (thats worth 0.200 in the 1/4 mile)"

Unsprung Weight, Part 2 - HondaSwap Forums