Wheel diameter

[Erich]

Thank you all for the advice. I should have clarified that the box is CR and it is a three speed. I do not know what the ratios are for 1st and 2nd. I do agree that the 19 inch wheels look better. However, I was planning on running the 19s on the road which is where the car will be most of the time. There is only this one hill climb here that accepts prewar cars, so I'm pretty limited for venues. Last year, there were only 5 prewar cars...a 6 1/2 liter Blower Bentley, a 3 liter Bentley, a Model T, a 1925 Amilcar and a 1910 Isotta.

[dickie65]

Hi,
I run a Type 65 with four speed CR gearbox ( only CR between third and fourth )
At Wiscombe with the VSCC I run either 3.25 x 19" dunlop bike tyres or 3.50 x 19" avon sm
With the MGCC at Wiscombe I run 3.25 x 17" avon sm on the rear and gain about 4 seconds in the dry.
The gain is due to being able to hold third gear through the Esses with the 17" and not losing speed just before Martini.
With the 19" I go between second and third through the Esses, 4 gear changes and the engine bogs in third before Martini.
The 17" rears are good through the Esses into second round Sawbench and third all the way up to Martini saving four or five gearchanges.
As It was really wet yesterday 9/9/17 I just ran with 3.50 x 19" Wheelspin off the line round Wis, Sawbench and Martini.
At Prescott the 3.50 x 19" avon were almost perfect for ratios.
For the Type 65 swapping rear wheels depending on venue works ( For VSCC events I am limited to what I can use within my class rules )
Its all trial and error, given complete freedom from rules you would have a set of different wheels for each venue to get the engine in its sweet spot.

Cheers Richard

[Erich]

Richard, what is the reason for running a 3.25 as opposed to a 3.50? Does the tyre spread over the wheel and ends up a lower profile...same grip but even lower ratio?

[dickie65]

Hi Erich,
The 3.25 x 17" Avon SM give the same tread contact but a lower ratio.
The tyre has quite a rounded profile until they have worn down a bit.
You should be able to check the overall diameter on line.
The 3.25 x 19" Dunlop has a lower profile thus lower gearing than the 3.50 x 19"
Have a look at motorbike tyre suppliers, The smaller section tyres also save weight.

Cheers Richard

[Erich]

I have confirmed that the car has "Ulster" ratios so I hope that the 17s with either 3.50s or 3.25s will do the job. Again, this is just one event in which I would like to prove the performance of Austin Sevens. I do wish there were more events here in NA that accepted prewar cars. I guess most places see anything built prewar as hopelessly old and unsuitable. I hope to change that view in my small way.

Best,

Erich

[Alan]

Unless the Amilcar is a C6 you should do ok among that lot.
I'd be careful about using narrow section bike tyres. They aren't really designed to accept the forces cars put into them. I'd use either sidecar tyres, or those designed for cars - available in the U.K.

[Mike Costigan]

In reply to the initial question of this thread, I'm sure I read somewhere that for some obscure reason some if not all export A7 Swallows had 17" wheels and their use may have applied to other export production models of A7s. This would bring the date of their production and use to well below the date of 1934 that Ruairidh mentions. I know this news made me more happy about my 'far from correct' Mk2 Swallow that for all its incorrectness looks quite comfortable with them and has good acceleration and speed to match.

Since no-one else has responded, I'll stick my head above the parapet! I would be very surprised if any Austin Swallows had 17" wheels. I have a 1933 Autocar Show Number which has a table with specifications of all the cars available on the UK market (ie for the 1934 season) and there is no car listed with 17" wheels of any size - I doubt if 4.00x17" tyres were available at that time, so certainly not for Swallows which had been discontinued by late 1933..

[Malcolm Parker]

[quote='My Ulster rep has the 5.25 axle ratio, a 3 speed box with a high 2nd (the 'Andes' box), and 3.50 x 19" wheels.  It is used for fast road use and has a similar spec engine to Steves car.  On the road it goes almost everywhere in top gear including hills of around 10% gradient. Second gear copes with all but the very steepest hills.  It will easily set off in second and pull away from a crawl in top.  Gearing is critical but so is weight reduction.  I am not a hillclimb expert but it seems that much depends on how high you dare rev your engine to in 2nd gear.

Unsurprisingly, I agree with what Alan says. My car which does OK but hasn't the most highly tuned engine out there has 3.50 x 19 tyres with a 5.25:1 CWP and 'fake' Ulster C/R 3 speed gearbox ratios. It's OK for most places but better for hillclimbs than sprints (and we do more of the former than the latter). Second gear is excellent and is the one used for most of the time on most of the hills we do. Only time I use top is on some sections of the longer hills on the Isle of Man. For sprints it's a bit different and I do have to use top. I don't, really, like to as gear changes cost time but it's either that, rolling off the throttle a little or revving the engine to places I don't want it to go to!! Snetterton Sprint next weekend will be something of a challenge in this respect!

Steve
[/quote]

[Steve Jones]

Unless the Amilcar is a C6 you should do ok among that lot.
I'd be careful about using narrow section bike tyres. They aren't really designed to accept the forces cars put into them. I'd use either sidecar tyres, or those designed for cars - available in the U.K.

Alan's warnings about motorcycle tyres are worth heeding particularly in cars used for competition - not that I would ever consider disagreeing with him when it came to tyres!!

However, I can say, been there, done that. My car still has the bruises to prove it and my shoulder has never, really, got fully better. Whilst the 'bike tyres it was on weren't 100% to blame for my Loton Park roll in 2014, they contributed to it significantly and I learnt my lesson the hard way. Tyres designed for car use only for me since then. My personal preference is for Longstones but other makes are, of course, available.

Steve

[Ian Williams]

I was on also bike tyres when I rolled four times at high speed in 2014, they were also not 100% to blame but contributed significantly, I won't bore you with my list of injuries but suffice to say I will never be the same again and neither will the car!