Sigma Supersport Gearbox / Altering 5 Speed Ratios

[James7]

The new Supersport with its 5 speed ‘sprint ratio’ gearbox seems to be getting some very good press at the moment.

 

Does anyone know what ratio changes have been made in the gearbox and which diff ratio is fitted (still 3.92)? I’d guess a higher first and second, possibly a lower 5th.

 

I’d be interested to know exactly what though as I’m thinking of having my 5 speed ‘box modified to better partner my standard 1.6 K Series.

 

As well as the short first gear, I find the gap between second and third too big and particularly noticeable on some track days. Third and fourth seem ok. 5th is good on the motorway / touring but may be better lowered slightly for track use.

 

The BGH‘2.8 Sporting Close’ looks to be an improvement over standard.

 

With their ratio options of 2.66, 1.75, 1.26, 1.0 and 0.86 and the 3.92 diff, GearCalc gives the following:

 

Gear Mph per 1000 RPM Mph @7000 RPM

----------------------------------------

1 6.20 43

2 9.43 66

3 13.09 92

4 16.50 115

5 19.18 134

 

Mph RPM (in Gears)

-------------------------------------------------

1 2 3 4 5

-------------------------------------------------

5 806 530 382 303 261

10 1612 1061 764 606 521

15 2418 1591 1146 909 782

20 3224 2121 1527 1212 1042

25 4031 2652 1909 1515 1303

30 4837 3182 2291 1818 1564

35 5643 3712 2673 2121 1824

40 6449 4243 3055 2424 2085

45 4773 3437 2727 2346

50 5303 3818 3030 2606

55 5834 4200 3334 2867

60 6364 4582 3637 3127

65 6894 4964 3940 3388

70 5346 4243 3649

75 5728 4546 3909

80 6109 4849 4170

85 6491 5152 4431

90 6873 5455 4691

95 5758 4952

100 6061 5212

105 6364 5473

110 6667 5734

115 6970 5994

120 6255

125 6516

130 6776

 

Gear Change RPM drop (change @7000)

---------------------------------------

1 -> 2 -2395 (to 4605)

2 -> 3 -1960 (to 5040)

3 -> 4 -1444 (to 5556)

4 -> 5 -980 (to 6020)

 

Some of the Ratios listed by Trans-X look interesting too. If I took their higher first and second ratios (2.48 and 1.69) kept 3rd and fourth as standard and the lower 0.86 5th gear, (as BGH option) the gaps between 1-2 and 2-3 would be reduced even further. First is still no higher than first in the Caterham 6 speed when fitted with the 3.62 diff (10mph is 1503rpm vs 1506rpm). GearCalc results as below.

 

Gear Mph per 1000 RPM Mph @7000 RPM

----------------------------------------

1 6.65 47

2 9.76 68

3 13.09 92

4 16.50 115

5 19.18 134

 

Mph RPM (in Gears)

-------------------------------------------------

1 2 3 4 5

-------------------------------------------------

5 752 512 382 303 261

10 1503 1024 764 606 521

15 2255 1536 1146 909 782

20 3006 2049 1527 1212 1042

25 3758 2561 1909 1515 1303

30 4509 3073 2291 1818 1564

35 5261 3585 2673 2121 1824

40 6012 4097 3055 2424 2085

45 6764 4609 3437 2727 2346

50 5122 3818 3030 2606

55 5634 4200 3334 2867

60 6146 4582 3637 3127

65 6658 4964 3940 3388

70 5346 4243 3649

75 5728 4546 3909

80 6109 4849 4170

85 6491 5152 4431

90 6873 5455 4691

95 5758 4952

100 6061 5212

105 6364 5473

110 6667 5734

115 6970 5994

120 6255

125 6516

130 6776

 

Gear Change RPM drop (change @7000)

---------------------------------------

1 -> 2 -2230 (to 4770)

2 -> 3 -1781 (to 5219)

3 -> 4 -1444 (to 5556)

4 -> 5 -980 (to 6020)

 

I’d hope that having BGH or similar changing 3 gear ratios should give a good close ratio gearbox with a higher 5th gear than top in the 6 speed but at significantly reduced cost compared to buying a used 6 speed, having it serviced / rebuilt if necessary and having the diff rebuilt to 3.62 ratio.

 

Any thoughts?

 

As an aside, do any of the sprint and hillclimb guys know whether this would cause any problems with eligibility for Class 1, should I look to compete in the clubs speed events?

 

And finally... while not looking to make this an excessively long post(!), for comparison the standard 5 speed and 6 speed results are shown below, all calculated with 185/60 R13 tyres

 

Cheers

 

James

 

_{Standard 5 speed with 3.92 diff:}

Gear Mph per 1000 RPM Mph @7000 RPM

----------------------------------------

1 4.91 34

2 9.12 64

3 13.09 92

4 16.50 115

5 20.00 140

 

Mph RPM (in Gears)

-------------------------------------------------

1 2 3 4 5

-------------------------------------------------

5 1018 549 382 303 250

10 2036 1097 764 606 500

15 3055 1646 1146 909 750

20 4073 2194 1527 1212 1000

25 5091 2743 1909 1515 1250

30 6109 3291 2291 1818 1500

35 3840 2673 2121 1750

40 4388 3055 2424 2000

45 4937 3437 2727 2250

50 5485 3818 3030 2500

55 6034 4200 3334 2750

60 6582 4582 3637 3000

65 4964 3940 3250

70 5346 4243 3500

75 5728 4546 3750

80 6109 4849 4000

85 6491 5152 4250

90 6873 5455 4500

95 5758 4750

100 6061 5000

105 6364 5250

110 6667 5500

115 6970 5750

120 6000

125 6250

130 6500

135 6750

 

Gear Change RPM drop (change @7000)

---------------------------------------

1 -> 2 -3229 (to 3771)

2 -> 3 -2127 (to 4873)

3 -> 4 -1444 (to 5556)

4 -> 5 -1225 (to 5775)

 

 

_{Standard Caterham 6 speed with 3.62 diff:}

Gear Mph per 1000 RPM Mph @7000 RPM

----------------------------------------

1 6.64 46

2 8.89 62

3 11.24 79

4 13.54 95

5 15.81 111

6 17.87 125

 

Mph RPM (in Gears)

----------------------------------------------------------

1 2 3 4 5 6

----------------------------------------------------------

5 753 563 445 369 316 280

10 1506 1125 890 739 632 560

15 2258 1688 1335 1108 949 840

20 3011 2250 1780 1478 1265 1119

25 3764 2813 2225 1847 1581 1399

30 4517 3375 2670 2216 1897 1679

35 5270 3938 3115 2586 2214 1959

40 6022 4500 3560 2955 2530 2239

45 6775 5063 4005 3325 2846 2519

50 5625 4450 3694 3162 2799

55 6188 4895 4063 3479 3078

60 6750 5340 4433 3795 3358

65 5785 4802 4111 3638

70 6230 5172 4427 3918

75 6675 5541 4744 4198

80 5911 5060 4478

85 6280 5376 4758

90 6649 5692 5037

95 6008 5317

100 6325 5597

105 6641 5877

110 6957 6157

115 6437

120 6717

125 6996

 

Gear Change RPM drop (change @7000)

---------------------------------------

1 -> 2 -1770 (to 5230)

2 -> 3 -1463 (to 5537)

3 -> 4 -1189 (to 5811)

4 -> 5 -1008 (to 5992)

5 -> 6 -805 (to 6195)

 

Edited by - James7 on 30 Dec 2011 22:17:53

[Grubbster]

I don't know what the ratios are in the Supersport, shame it doesn't state what they are on the website.

 

When I changed my gearbox internals I went to Steve Perks (SPC) and he built me a brilliant 'box with great ratios for my car (too tall for a standard 1600) and I've been very pleased with it. Long first, long second and slightly shorter 5th. On my slicks (larger diameter than my CR500's) it exceeds 60 in first and 90 in second! Just a tad less than this on road tyres. It's worth talking to Steve though, if just to get a comparison or opinion on what you want to do. For me it turned into a very expensive conversation though . . . 😬

 

Differential Ratio: 3.92

1st Gear Ratio: 2.482

2nd Gear Ratio: 1.61

3rd Gear Ratio: 1.225

4th Gear Ratio: 1

5th Gear Ratio: 0.82

[Jason Plato]

but on the road you only have a 2 speed gearbox

 

shirley that cant be fun

[Grubbster]

Quoting Dave Jackson: 

but on the road you only have a 2 speed gearbox

 

shirley that cant be fun

 

In theory you are right of course but it is still quite fun. On track it comes into its own though, it really is good then, so much better than the standard 5 speeder. Not sure what it would be like with a 6 speed box, never tried one, I didn't fancy it for touring. To be honest as a road car it is not as good as it was when I had less power, it is just too quick to really enjoy on todays roads. This problem will be resolved though when my Sigma 125 Academy car arrives in about 9 months time!

[The Prism-er]

Are SPC still around?

They did some work on my gearbox but Steve seems very difficult to contact these days.

[Paul McKenzie]

I saw Steve a couple of months ago when he built me a new box, and I've spoken with him several times since. He had loads of work on then, so I'm sure he'll call you if you leave a message.

[Boss Hogg]

My diff says 3.91 on it. No idea what the ratios are. Will be able to comment on the box once I've finished the build!!

[David Lynch]

Sure it would push you in Class 2 with the Six Speed/Supersported 1.6 K's

Worthwhile upgrade given relative cost of boxes but I'd consider the influence of the engine upgrade path too.

 

Spend sod all and come play in class one for a year

[Paul McKenzie]

Quoting Grubbster: 

I don't know what the ratios are in the Supersport, shame it doesn't state what they are on the website.

 

When I changed my gearbox internals I went to Steve Perks (SPC) and he built me a brilliant 'box with great ratios for my car (too tall for a standard 1600) and I've been very pleased with it. Long first, long second and slightly shorter 5th. On my slicks (larger diameter than my CR500's) it exceeds 60 in first and 90 in second! Just a tad less than this on road tyres. It's worth talking to Steve though, if just to get a comparison or opinion on what you want to do. For me it turned into a very expensive conversation though . . . 😬

 

Differential Ratio: 3.92

1st Gear Ratio: 2.482

2nd Gear Ratio: 1.61

3rd Gear Ratio: 1.225

4th Gear Ratio: 1

5th Gear Ratio: 0.82

 

Think you might be wrong on the 90 in second

 

I have the same 4 ratios in an SPC box and it works out something like this:

 

CR 13 INCH WHEELS/yoko 048

mph circ rpm ratio final drive mph/1000rpm

44 5.40 7000 2.48 3.92 6.3

68 5.40 7000 1.61 3.92 9.7

89 5.40 7000 1.23 3.92 12.8

110 5.40 7000 1.00 3.92 15.7

117 5.40 6500 0.87 3.92 18.0

 

So 90 in third is maybe more like it ....unless you're using 9K rpm

 

 

 

 

 

Edited by - Paul McKenzie on 31 Dec 2011 17:02:14

[Dignity]

Try 8,500rpm and 205/60x13. I think thats what Grubbsters revs to?

 

Edited by - Dignity on 31 Dec 2011 17:13:15

[Paul McKenzie]

I stand corrected . I think I need to dig out my slicks and measure them...I may be going quicker than I thought.

[Grubbster]

Yes I limit it to 8600 rpm at the moment but 9000 is probably about as high as it would go. I can't remember the size of the slicks but they are a lot bigger diameter than anything else I have ever fitted, the CR500's look tiny in comparison. On CR500's at Llandow I was still getting a bit of wheelspin on the straight in 3rd and then 4th gear over the bumps , you can hear the revs 'blip' in the video as I go along the pit straight

and I rarely went over 8000 rpm!

[James7]

Thanks all. If it would put me into class 2 I’ll postpone this upgrade and look to come and have a go in Class 1 first, thanks David.

 

Look forward to hearing your thoughts once built though Boss Hogg!